The reason of decline of Leatherback turtles (Dermochelyscoriacea) in French Guiana: an hypothesis
Johan Chevalier^1,2,3, Xavier Desbois² and MarcGirondot^1,2
1- URA 1337 - Evolution et Adaptations des SystèmesOstéomusculaires, CNRS and University Paris 7, 2 place Jussieu, 75251Paris cedex 05, France.
2- Réserve de l'Amana, 97361 Awala-Yalimapo, Guyane française.
3- WWF-France, 151 boulevard de la Reine, 78000 Versailles, France.
French Guiana is located 400 km north-west of the Amazon River estuary. It isthe most important Leatherback turtle (Dermochelys coriacea) nesting zone inthe world, comprising about 40% of the world's nesting Leatherbacks. During thelast decade, all the other known major nesting beaches for D. coriacea,i>D. coriacea,in Mexico, Irian Java or Malaysia have displayed a decline in the total numberof nests laid during the nesting season. Within this context, the trend of thenesting Leatherback population in French Guiana has strong implications for theglobal long-term survival status of this species. A 30 year reconstruction ofthe total numbers of nests deposited at the beach reveals three distinctperiods: an increase in total nests from 1967 to 1988, relative stability from1988 to 1992, and a decrease since 1992. The increase from 1967 to 1988 is wellexplained by a change of nesting beach of females from west to east. However,the recent decline does not appear to be due to the same phenomenom as no newlarge nesting beaches have been observed in this region. We have evaluated theyearly net production of female juveniles per nesting female on this beach. Itappears to be drastically low, from 7 to 14 female juveniles per year and pernesting female. Such A low value probably reflects an inadequate level ofhatchlingl ofhatchling production, with respect to population renewal. Hatchlings andjuveniles suffer high levels of predation (catfish and sharks for the mostcommon marine predators). Sexual maturity is reached 9 years after hatching.Therefore, a high level of hatching production is needed to ensure enoughoffspring survive to maturity. With this in mind, we propose the followinghypothesis to explain the changing trends in numbers of D. coriaceanests on Ya:lima:po beach over the last 30 years. From 1967 to 1988, a changeof nesting beach by the nesting females of the region has concentrated most ofthem on the Ya:lima:po beach. However, this beach is not ideal for incubationof eggs, As only 4 to 10% of the nests have produced hatchlings. Therefore, therenewal of the female population was not achieved and an ensuing decline isactually observed. This decline could be enhanced by changes in techniques usedby shrimp fisheries. There are several possible factors that could havecontributed to the low level of hatchling production of nests on the beach butcurrently, no data are actually available to differentiate among them.